Donald S. Mavinic

Maintaining nitrite build-up in a system acclimated to free ammonia

The objective of the research program was to study process changes that could be used to maintain nitrite build-up and overcome the effects of acclimation to free ammonia (FA) and allow the use of a shortened nitrification/denitrification pathway for nitrogen removal from highly nitrogenous wastes. The study employed bench-scale, activated sludge cells. Measures investigated to overcome the effects of acclimation were: (1) increasing MLSS wastage by a factor of five; (2) extension of contact time to high FA levels to 50% of the total retention time; (3) raising FA concentrations to 40 mg NH3-N/l; (4) use of a more complex substrate (municipal landfill leachate); (5) double substrate inhibition (FA and sodium chlorate); (6) provision of internal denitrification; and (7) temporary reduction of FA levels. Of these, the most effective was internal denitrification.

Controlling factors for simultaneous nitrification and denitrification in a two-stage intermittent aeration process treating domestic sewage

Abstract This bench-scale research investigated the controlling factors for simultaneous nitrification and denitrification (SND) in a 2-stage, intermittent aeration (IA) process, designed for nitrogen and phosphorus removal. The 2-stage process consisted of an anaerobic zone followed by an oxidation–reduction potential (ORP) controlled, intermittently aerated, completely mixed (IACM), tank. The three independent variables examined were the average ORP level, organic substrate (acetate and methanol) dosage and aeration cycle. The sewage used was completely of residential origin. Nitrogen balance clearly indicated that the nitrogen loss, due to SND in the aeration tank, contributed 10% to 50% of the influent TKN to the overall nitrogen removal. Significant differences in both nitrification and denitrification in the IACM tank were observed, when different average ORP levels were applied to the aeration control; this proved that absolute ORP can be used as a real-time control parameter for SND. Under low DO and intermittent aeration conditions, acetate and methanol additions improved nitrification over the entire dosage range and denitrification at relatively low dosages. Finally, a longer aeration cycle, with a zero-DO period, appeared to favor sequential nitrification and denitrification (SQND), not SND.

Benefits of using selective inhibition to remove nitrogen from highly nitrogenous wastes

Abstract Continuous‐flow, activated sludge systems and a batch test showed that nitrite reduction rates were 63% higher than nitrate reduction rates; COD consumption rates were 40% lower for nitrite reduction than for nitrate reduction; and biomass production up to 300% lower with the reduction of nitrite than with nitrate. Nitrite build‐up was achieved by selectively inhibiting the nitrite oxidation step.

The effect of decreased ambient temperature on the biological nitrification and denitrification of a high ammonia landfill leachate.

This research investigated the nitrogen removal capabilities of a pre- and post-denitrification process, when treating sanitary landfill leachate containing an ammonia concentration of over 2200 mg N/L, at operating temperatures down to 10 degrees C. The treatment system employed is generally known as a 4-Stage Bardenpho process. Two parallel systems were operated throughout the study; each system had an aerobic solids retention time of 20 days and an external recycle ratio (return activated sludge) of about 3:1. During the entire experimental period, one system used an internal recycle ratio of about 4:1, while the other system used one of 3:1. Methanol was used as supplementary carbon source for denitrification. When operating temperature was decreased from 20 to 17 degrees C, an approximate 15% decrease in denitrification was immediately experienced within both systems, with no noticeable affect on nitrification. This was an unexpected result. Subsequently, the temperature was further decreased to 14 degrees C, and finally to 10 degrees C. With the temperature at 14 degrees C, aerobic wasting was also stopped and methanol loading was progressively decreased to match actual denitrification requirements. At 10 degrees C, both systems suffered major nitrification and denitrification inhibition. Changes in operating parameters, such as a decrease in influent ammonia and methanol loading, as well as an increase in ambient temperatures, from 10 to 15 degrees C, did not significantly improve overall system performance, within a reasonable time frame. Both denitrification and nitrification problems were mainly attributed to decreased ambient temperature, although other possible factors were noted; at project completion, about 50% of the incoming ammonia was being removed across the system.

A SOLUBILITY AND THERMODYNAMIC STUDY OF STRUVITE

Accumulation of magnesium ammonium phosphate hexahydrate (struvite) on surfaces in contact with wastewater, especially in anaerobic sludge digestion and post-digestion processes, is a widely reported problem in the wastewater treatment industry. The solubility and thermodynamic properties of struvite at different temperatures was studied. Struvite thermodynamic solubility products at temperatures between 10 and 60 °C were determined by variation of solution ionic strength and extrapolation to zero ionic strength, using an appropriate activity coefficient model. The pKsp value of struvite at 25°C was found to be 13.36(±0.07). The pKsp value for a temperature range of 10-60 °C varies from 14.36(±0.05) to 14.01(±0.03) with the minimum value of 13.17(±0.05) at 30°C. The effect of ionic strength, pH and temperature on struvite solubility was also studied. The solubility of struvite determined in deionized water was found to be 169.2 (±4.3) mg l-1 at 25°C, with the maximum value of 212.7 (±3.8) mg l-1 at 35°C. Standard enthalpy of reaction, ΔHγ °, calculated from the average Ksp values for the temperature range of 10-30 °C, was 23.62 Kcal mol-1. An analytical expression for the Ksp as a function of temperature has been developed by fitting experimental data.

Methanol-induced biological nutrient removal kinetics in a full-scale sequencing batch reactor.

The primary goal of this research was to determine the potential for denitrification and phosphorus removal of a full-scale sequencing batch reactor (SBR), with and without the use of methanol as an external carbon source. The control SBR, without methanol addition, achieved negligible denitrification. Two denitrification rates were observed in the experimental SBR, with methanol addition, an initial fast rate and a slower second rate. The denitrification rate during the first rate period increased with increasing methanol concentration, until a maximum denitrification rate of approximately 19 mg NOx-N/g MLVSS/day was attained. Following the depletion of the methanol, denitrification reactions probably continued by using the available natural carbon in the influent, resulting in a slower, second denitrification rate. Biological phosphorus uptake and release was significant only in the SBR with methanol addition. Methanol was probably not utilized as the carbon source for the enhanced biological phosphorus removal (EBPR) process. However, methanol addition was critical, since it depleted the available nitrates and thus allowed EBPR to take place.

Autothermal Thermophilic Aerobic Digestion (ATAD)-Part I: Review of Origins, Design, and Process Operation

Increased legislative constraints have fuelled an interest in developing sustainable and economical methods for sludge digestion. Autothermal thermophilic aerobic digestion (ATAD) is a robust process that produces Class A biosolids from a wide range of organic sludge (e.g., animal waste, sewage sludge, food processing waste etc.). The advantages of this technology include good biomass biodegradation, pasteurization and process stability. Thermophilic temperatures result from the metabolic heat released by microorganisms during digestion. Efficient aeration and mixing are needed in addition to adequate reactor insulation to maintain thermophilic temperatures. Significant advances have been made in the optimization and adaptation of ATAD technology since it was first introduced in the early 1970s. Continuing innovation and advancement of the process is reflected in the number of patents for “next” generation technologies. Despite the apparent benefits of this process, ATAD is still not well understood. This...

Experiments using Daphnia to measure landfill leachate toxicity

Abstract Leachate from municipal refuse was analysed for acute toxicity using Daphnia pulex, rainbow trout (Salmo gairdneri) and sockeye salmon (Oncorhynchus nerka) as test organisms. Procedures used in conducting the daphnia bioassay are detailed. The 3 1 2 - year testing program was designed to compare daphnia bioassays with standard fish bioassays and residual oxygen bioassays (ROB). The results from the daphnia bioassays compared favourably with the standard fish bioassay results. No disadvantages could be seen in using daphnia rather than fish as test organisms for determining the acute toxicity of municipal refuse leachates. However, both financial and logistic advantages could be gained by using daphnia rather than fish.

Real-Time Control of Two-Stage Sequencing Batch Reactor System for the Treatment of Animal Wastewater

An evaluation of the use of ORP as a real-time control parameter was conducted. A newly developed real-time control strategy, using ORP, was successfully applied, without a supplemental carbon source, to a new type of bench-scale two-stage SBR process for the treatment of swine wastewater. With real-time control, consistently high system performances were obtained, despite the fluctuation of influent quality; removal efficiencies for BOD5, COD, NH4-N, TKN, Ortho-P, Total Phosphorus (TP) averaged approximately 99.6%, 97%, 98%, 96%, 95% and 94%, respectively. Also, effective denitrification could be achieved without the addition of an external carbon source; the average NOx-N level on final effluent was 11 mg l−1. The data from this study reveal that both the ORP and pH can be used as successful process control parameters in the optimization of nutrient removal and treatment system capacity. Feasible real-time control strategies using dynamic ORP and pH change are established through this research.

Effects of various process parameters on struvite precipitation kinetics and subsequent determination of rate constants

In this paper, struvite (MgNH(4)PO(4).6H(2)O) precipitation kinetics were studied with different operating conditions (varying supersaturation, pH, Mg:P ratio, degree of mixing and seeding conditions) and relevant rate constants were determined by fitting a slightly modified first-order kinetic model to the experimental data obtained. The rate of change of ortho-P concentration in the bulk solutions increases with increasing supersaturation ratio. The estimated rate constants are 2.034, 1.716 and 0.690 hr(-1) for the supersaturation ratio of 9.64, 4.83, and 2.44, respectively. Kinetic parameters were also evaluated for the Mg:P ratio between the ranges of 1.0 and 1.6, indicating higher phosphorus removal efficiency with increasing Mg:P ratio. The rate constants were found to be 0.942, 2.034 and 2.712 hr(-1) for Mg:P ratios of 1.0, 1.3 and 1.6, respectively. The experimental observations for kinetic study of struvite precipitation with different stirrer speeds clearly show that the mixing intensity used had little effect on the intrinsic rate constants. K values found to be 2.034 and 1.902 h(-1) for 100 and 70 rpm, respectively. Seeding, with 250-500 microm of seed crystals during the struvite precipitation kinetics test, was found to have very little effect on the ortho-P removal.